The decontamination of contaminated soil and/or ground water is an important topic of current interest. Many technical methods have already been developed as solutions. Because the areas to be decontaminated are often developed areas, the so-called in-situ methods are particularly important because they provide decontamination of the contaminated soil and/or water on-site without having to excavate the relevant soil region.
A particularly effective method for the in-situ decontamination of soils which are contaminated with organic pollutants is so-called in-situ chemical oxidation (ISCO). The functional principle of in-situ chemical oxidation is based on suitable chemical oxidants being introduced into and distributed in the soil. Therefore, in particular petroleum-derived hydrocarbons, aliphatic hydrocarbons, volatile chlorinated/halogenated hydrocarbons or even polycyclic aromatic hydrocarbons in the soil can be degraded. Owing to chemical reactions of the oxidant in the soil, oxygen is released, whereby degradation processes are promoted and accelerated, in order to eliminate the present pollutants in-situ. The method is explained, for example, in the publication “In-situ chemische Oxidation: Erfahrungen aus der Herdsanierung”(Handbuch zur Altlastensanierung, C. F. Müller Verlag, 3rd edition, February 2011). Furthermore, the use of ISCO for in-situ decontamination of soils is described in DE 20 2010 005 812 U1 which provides seminal disclosure regarding this technology.
In-situ chemical oxidation is particularly suitable for source-zone decontamination in response to average to high concentrations of pollutants. A particular advantage of in-situ chemical oxidation over alternative known methods is the shortened decontamination time. The oxidant is introduced into the decontamination areas using hydrostatic pressure and is injected into the soil region to be treated, for example using injection lances, as described in DE 20 2010 005 812 U1.
Although the method is, in principle, highly suitable for soil decontamination, it has been shown in practice that the soil decontamination with the aid of in-situ chemical oxidation using conventional injection lances does not produce the desired success. This is due to the fact that when injecting the oxidant using conventional injection lances, the reagents often do not sufficiently penetrate into the soil to be treated, and therefore co-reactants frequently do not come into reactive contact and as a result the amount of decontamination is often insufficient. The chemical degradation of the pollutants occurs instead via a second order reaction. This means that at low concentrations of the oxidant or the pollutant, the degradation rate is also greatly reduced. Owing to inhomogeneous soil properties, heterogeneous pollutant distributions and the pollutant properties themselves, which are often difficult to predict, an increased active radius of the oxidant is required in many situations, which cannot be achieved with the conventional injection technology. In particular, it has been established that in the presence of soil layers having low hydraulic permeability and/or of rock formations, satisfactory decontamination cannot be achieved because such poorly permeable soils cannot be successfully decontaminated or require extremely long decontamination time periods, due to the extremely low flow speeds of the groundwater.